A side-entry fill valve takes its supply through the side wall of the cistern, typically a few centimetres up from the base, with the water pipe running horizontally into the tank. This is the older and still very common arrangement in UK homes, particularly where the supply pipe rises through a wall cavity or runs along a skirting board before turning up into the cistern. Side-entry valves are usually the easier option where floor space beneath the cistern is tight, since there is no need for the pipe to come straight up from below.

The flush plate itself is usually the first point of failure a customer notices, whether that is a button that has stopped actuating, a plate that has come loose from the wall, or a dual-flush mechanism that only performs a full flush regardless of which button is pressed. Because the plate connects to the cistern through a spindle or cable rather than sitting directly on top of it, the fault could sit at the plate, along the linkage, or at the flush valve itself, and each of those needs a different part.

A siphon uses the physics of siphoning rather than a simple valve seal to move water from the cistern into the pan. Lifting the lever raises a plastic or rubber diaphragm inside the siphon body, which pushes a slug of water up and over a bend in the siphon tube, starting a siphoning action that then draws the rest of the cistern's contents down through the tube by suction until the water level drops low enough to break the siphon and stop the flush. This is why older cisterns produce that distinctive extended flush sound rather than the quicker valve-open, valve-close action of a modern flush valve.

More information is available at trade plumbing supplies.

A flush valve, by contrast, works as a straightforward seal at the base of the cistern that lifts to let water fall directly through into the pan under gravity, plumb2u.com with no siphoning action involved, and shuts again once the float or timer mechanism allows it to reseat. Flush valves are what almost all dual-flush cisterns use, since a siphon's all-or-nothing action makes a genuine short flush difficult to achieve, whereas a valve can simply be held open for a shorter or longer period.

Before placing an order, it pays to note three things on site: whether the cistern sits flush to the pan or is wall-mounted above it, the fill valve's body length if there is a tight fit inside the tank, and whether the existing lever operates through the lid or via an external arm. Plumb2U carries fill valves, flush valves and levers suited to both close-coupled and low-level cisterns, stocked at trade prices for plumbers who need to get the right part on the first order rather than the second. Trade supplies despatch from Plumb2U's Epsom base to plumbers across the UK, and Plumb2U remains a straightforward call when the cistern type is not obvious from the pan alone.